Contractors doing construction or renovation work, such as installing kitchen cabinets, usually need both a miter saw for making accurate angled cuts across workpieces, and a table saw for performing straight cuts along large workpieces. Two saws clutter up the workplace, especially if it is confined. Also, it is a nuisance to transport two saws from site to site. Furthermore, professional quality saws are quite expensive. It is therefore desirable to have a saw which can perform both functions.
The prior art contains various examples of convertible saws which may be used in a first mode as a miter saw, or sometimes as a simple chop saw for making perpendicular cuts across workpieces, and in a second mode as a table saw. An early example, U.S. Pat. No. 1,924,672, issued Aug. 29, 1933 to Zachara, shows a type of convertible saw, which, to my knowledge has not been commercially adopted. This is a complex saw which provides mitering, cutting off, squaring, dadoing of convex or concave surfaces, tenoning, grinding or ripping, all saw operations being performed with a single circular saw blade. It includes abase unit having rails along which upper parts carrying the saw can run to perform cutting off. On this base unit is mounted an upper base unit having a vertical axis swivel carrying a horizontal axis pivot about which an arm carrying the saw and motor combination is mounted; this provides the miter cutting. Above this arm and saw/motor combination is a saw table, which is pivotally mounted so that it can be lifted up to allow mitering and other operations without interference, and can be lowered to a horizontal position, when the saw is suitably aligned to protrude through a slot in the table, in which position the saw can operate as a table saw.
In the Zachara design, the saw is belt-driven by a motor which is behind the swivel axis of the saw arm, while the back guides against which workpieces are held for miter cutting are well in front of the swivel axis. With this design it would seem that the miter angles which could be cut would be rather restricted. A further disadvantage is that, because the saw is intended to be used in so many different ways, including use as what amounts to a radial arm saw, it is very complicated and would not be particularly portable. Consequently, it would be of little or no use to a contractor who wished to use a single miter/table saw to do construction or renovation work at a customer's premises.
Present day miter saw designs differ considerably from Zachara's design in that they have compact gear drives, and swivel tables of the turntable type. Convertible versions of these saws may conveniently be described as “flip-over” saws, which have a base frame which pivotally supports the combination of a circular saw assembly and saw table, this combination being capable of being flipped over through 180°. In a first orientation, the saw assembly is above the table and has a handle by which it may be pressed down towards a slot in the table to perform chop or miter cuts. In the second orientation, the saw assembly lies below the table and can be fixed in position under the table to protrude through the slot, and so is usable as a table saw. “Flip-over” saws of this kind are represented by the following U.S. patents:                U.S. Pat. No. 5,960,691, issued Oct. 5, 1999 to Garuglieri;        U.S. Pat. No. 5,787,779, issued Aug. 4, 1998 to “ ”;        U.S. Pat. No. 5,570,641, issued Nov. 5, 1996 to “”;        U.S. Pat. No. 5,513,548, issued May 7, 1996 to “ ”;        U.S. Pat. No. 5,189,937, issued Mar. 2, 1993 to it ”;        U.S. Pat. No. 4,531,441, issued Jul. 30, 1985 to Bergler;        U.S. Pat. No. 3,570,564, issued Mar. 16, 1971 to “ ”;        U.S. Pat. No. 2,851,068, issued Sep. 9, 1958 to Goodlet.        
The “flip-over” design has some drawbacks. Firstly, the base frame has to be fairly large to provide space which allows the table and motor-saw blade combination to flip over through 180°, so such designs tend to be somewhat cumbersome. Also, the motor-saw blade combination is heavy, so the pivot mechanism must be robust and the user may find it awkward to switch from one mode to the other.
Another problem is that some of the most desirable miter saws are not adaptable to the flip-over design, since the saw table is in the form of a turntable having the required saw slot. This turntable also has structure below the slot, used for mounting or moving the turntable, which structure would not allow the miter saw to be inverted and used as a table saw. Such miter saws include those manufactured by Makita Corporation, for example that shown in U.S. Pat. No. 4,638,700, issued Jan. 27, 1987, which is otherwise a desirable type of miter saw for professional work. The turntable structure shown in FIG. 2 of that patent would not allow the saw blade to project through the turntable, so it would be unsuitable for use in a “flip-over” convertible saw design.